It’s déjà vu all over again, with the Black-and-Gold M.A.S.H back in full duty — much like the first two months of the season.

Three top players on the sidelines in Patrice Bergeron, Tuukka Rask and Charlie McAvoy. The first two appear shorter term. The latter the cause for most concern with the rookie defenseman and Calder Trophy candidate out at least four weeks with a sprained left MCL, sustained just 37 seconds into this past Saturday’s 2-1 OT win.

Tuesday night, the Detroit Red Wings came to town to face a newer-looking Bruins roster compared to the one that had swept all three previous encounters this season: Rick Nash, Brian Gionta, Tommy Wingels and Nick Holden all available, Matt Grzelcyk back in McAvoy’s slot, Tommy Wingels in for Noel Acciari.

Here’s what we learned from a game that started like a cakewalk and ended anything but, as the B’s twice surrendered two-goal leads but nonetheless completed a second consecutive four-game sweep of a season series.

Both goaltenders shell-shocked in sloppy opening 20

In a wild start, Red Wings goaltender Jared Coreau, making his first NHL appearance of the season, conceded two goals on his first two shots on goal. Just 27 seconds in, Torey Krug launched a left-point slap shot that found the back of the net for his 12th of the season; Brad Marchand and Holden assisting. Fifteen seconds later, Jake DeBrusk intercepted a Wings outlet pass and danced back into the Wings zone with a cue-ball shot off Jonathan Ericsson’s stick that dribbled by Coreau for his 14th.

Khudobin, in fact, fared only one shot better than his opposite number; the Black and Gold netminder coughed up the next two from the first three shots on him. Frans Nielsen’s power-play goal pulled the Wings to within one at 2:16, and Mike Green drove the equalizer home at 7:53.

Coreau’s night was brought to an abrupt end 3:27 into the middle period, when Marchand increased the Bruins’ lead to 4-2 with a finish down low off Krug’s pass for his 26th of the season. Former UMaine standout Jimmy Howard replaced the hapless Coreau for the next 36 minutes and change.

“Forget about it and just flush away,” Coreau said postgame. “I just need to bide my time in practice and look at the video, and see what I got to work on and go from there. Like Conor McGregor says when he fights, you win or you learn. So I did a lot of learning tonight.”

Shoddy defense costs Bruins a regulation victory

Marchand’s second tally of the game, at 13:18 in the middle stanza, put Boston’s offense at 17 goals and counting in three of their last four games. Problem is, they’d also given up 11 and counting in as many contests after Zdeno Chara lost the handle in his slot, allowing Anthony Mantha to pick his pocket and finish past Khudobin for his own brace at 15:40.

To complete the strain of erroneous defending, David Krejci inadvertently deflected a Martin Frk shot past Khudobin at 9:46 of the final frame to knot the game at 5-5.

“We didn’t play our best through the neutral zone,” Marchand assessed about the goals given up. “We didn’t take care of the pucks the way we should have, and we didn’t win enough board battles. It wasn’t our best game and it won’t be every night, especially in this stretch right here. But if we expect to win, we can’t continue to play like that.”

Marchand completes “trick” in OT

Last Tuesday, the Bruins took out Carolina in OT; Saturday, they handed Montreal the same fate.

Like the Montreal outcome, Marchand sealed the win Tuesday night with a hat-trick clincher when he scooped up a Krug rebound and backhanded it past Howard just 34 seconds into OT.

“I was chuckling after the game,” head coach Bruce Cassidy said, “because, you know, there he is, puck finds him. But he’s on it, doesn’t quit. [He] made some real nice plays tonight.”

The goal notched Marchand’s third career hat trick and fourth ever five-point night.

“I was kind of hoping that Torey was going to get it there for the hat trick,” Marchand admitted about the game-winner, “but it ended up on my stick and luckily it went in. You have to be able to play those games, even when we didn’t play our best tonight. We got two points, which is really all that matters.”

Krug comes up big in McAvoy absence with career-high four points

“Being a Michigan guy,” Cassidy said about Krug’s contribution against Detroit, “I think it shows every time he plays them [the Red Wings]. [The] power play, now, is a little crisper. We’ve changed it a bit. Obviously, he takes a lot of credit, should get a lot of credit for that.”

Krug, who has 18 points (6 goals, 12 assists) in his last 15 games, did everything but kill penalties. In the absence of McAvoy, Krug logged 20:18 of ice time — 4:46 of which came on the man-advantage.

“It’s a team that I get excited to play against,” Krug said about his epic night against the Wings. “A lot of friends and family are watching back home. I’ll probably show back up and get a lot of angry text messages, but at the end of the day it’s just another in-division team.”

As for filling in for McAvoy’s role:

“You want to be the guy who they put more on your shoulders, and more on your plate in front of you,” Krug said. “Definitely, the last time he [McAvoy] went out of the lineup, I felt like I took another step in the right direction in my game.”